1. Field of the Invention
The invention relates to the technical field of voltage conversion, particularly to a circuit system for driving a high-intensity discharging lamp.
2. Background of the Invention
In the past, the lamp set of a vehicle is comprised of traditional tungsten filament lamps. In 1992, Philips Company promoted a high-intensity discharging lamp (HID), which changed the illumination history of the human being. The high-intensity discharging lamp (HID) is mainly a xenon lamp set or a gas discharging lamp set. As compared with the traditional lamps, the HID lamp has the advantages of high intensity, high color temperature and stability in beam pattern. The enhancement of the intensity indicates a wider visible range when driving a vehicle in night, the high color temperature indicates more real color of the viewing object and the stability of beam pattern represents a fixed illumination range such that the driver does not need to worry about instant moving of the illumination range of the head lamps.
In the traditional lamp, the light is produced by heating the tungsten filament when flowing the current therein. In the HID discharging lamp, a DC voltage is boosted and converted into a switching AC voltage of 23,000 volts through a drive circuit system, rendering liberation of electrons of the xenon gas in a crystal glass lamp after high voltage oscillation and producing a light source for illuminating intensive arc between two electrodes, and then, the drive circuit system will lower the operating voltage to 80-110 volts after smooth activation.
FIG. 1 shows a drive circuit system 100 for a conventional HID lamp. The drive circuit system 100 in FIG. 1 uses a flyback converter. As switch S1 is turned on, the voltage of terminal A is in a low potential and energy is stored in transformer T1. As the switch S1 is turned off, the energy stored in the transformer T1 is released in a form of current at the secondary of the transformer T1. The voltage induced at the secondary of the transformer T1 is reflected to the primary of the transformer T1. If the winding ratio between the primary of the transformer T1 and the secondary of the transformer T1 is N1/N2=n and the voltage of the secondary of the transformer T1 is Vo, due to reflection of the voltage of the secondary, Va, the voltage at terminal A, becomes as follows: Va=Vin−(−nVo)=Vin+nVo. FIG. 2 is a schematic diagram the voltage of a conventional drive circuit system 100. As shown in the drawing, the voltage at terminal A is not merely Vin+nVo. Meanwhile, due to equivalent inductance of the transformer T1, a spark will occur at the terminal A, as shown in the circle of FIG. 2, which will result in exhausting of the energy and cause damage to the switch S1. Aiming at the reflection phenomenon of the voltage at the secondary of the transformer T1, the conventional technique adopts a switch having higher withstanding voltage. However, it will increase more costs. Another approach is to use a clamp circuit to clamp the voltage reflected from the secondary of the transformer T1 so as to protect the switch S1. However, it will result in lowering conversion efficiency of the transformer T1. Therefore, it is desirable to provide an improved circuit system for driving a high-intensity discharging lamp to mitigate and/or obviate the aforementioned problems.